Hazelnut meal was evaluated as an alternative protein source to fishmeal in diets for rainbow trout, Oncorhynchus mykiss (initial wt 57.5±0.1 g). Hazelnut meal was incorporated in the diet at levels of 0% (control), 7.5%, 15%, 22.5%, and 30%. Diets were tested in triplicate for ten weeks. Higher levels of hazelnut meal produced better growth performance, that was sig- nificantly higher in fish fed 30% hazelnut meal than in the control (p<0.05). Feed utilization and protein efficiency ratios followed a similar trend while the level of hazelnut meal did not significantly affect whole body composi- tion. Apparent digestibility of dry matter and energy of fish fed hazelnut meal at all levels was significantly lower than in fish fed the control (p<0.05). Crude and digestible protein, as well as energy retention, were significant- ly correlated with hazelnut meal level. Nevertheless, energy retention declined in fish fed 30% hazelnut meal. Based on growth performance and nutrient retention, the optimal level of hazelnut meal in diets for rainbow trout may be around 30%.